Ceramic anode solid oxide fuel cell

ABSTRACT

A solid oxide fuel cell having a cathode, at least an electrolyte membrane, and an anode having a ceramic material and an alloy of nickel and at least a second metal, the alloy having an average particle size not higher than 20 nm.

The present invention relates to a solid fuel cell, to a cermetmaterial, to the process for the preparation of said cermet, and to amethod for producing energy using such cell.

Solid-oxide fuel cells (SOFCs) convert chemical energy into electricalenergy with high efficiency and low emission of pollutants. Although theintroduction of a “green energy” might seem an attractive scenario, itsimplementation is beset with technical and economic difficulties.

The most common anodes materials for solid oxide fuel cells comprisenickel (Ni) cermets (ceramic and metallic composite materials) preparedby high-temperature calcination of NiO and ceramic powders, usuallyyttria-stabilized zirconia (YSZ) powders. These Ni-cermets perform withH₂ fuels and allow internal steam reforming of hydrocarbons if there issufficient water in the feed to the anode. Because Ni catalyzes theformation of graphite fibers in dry methane, it is necessary to operateanodes at steam/methane ratios greater than 3, as from WO 00/52780 (inthe name of Gas Research Institute).

S. J. A. Livermore et al. Journal of Power Sources, vol. 86 (2000),411-416, refers to a cermet anode for SOFC made of nickel andceria-gadolinia (CGO). This anode performs at 600° C. using 10% H₂/N₂ asthe fuel.

A. Müller et al., Proc. of the 3rd European Solid Fuel Cell Forum,Nantes France, June 1998, 353-362, relate to a Ni-YSZ anode fuel cell.It is envisaged a degradation of the anode related to microstructuralchanges occurring during operation. The nickel particles have a meandiameter of about 0.5 μm, and are homogeneously distributed in theanode. After long term operation at high current density and fuelutilization (H₂+H₂O), the agglomeration of the nickel particles leads toa decrease of the amount of three-phase boundary (TPB), resulting in anincrease in the anode losses.

A. C. Müller et al., HTMC IUPAC Jülich 2000 suggest that the degradationdescribed by the previous document could be prevented by a multilayeranode whose divers layers differ in their microstructure to fulfill thelocally different requirements for SOFC anodes. In particular, thecontent of Ni and the Ni particle size should increase from first layer(that in contact with the electrolyte) to last layer, thus increasingelectronic conductivity, TEC (Thermal Expansion Coefficient) andporosity. The YSZ content should simultaneously decrease. The cermetsamples were prepared by mixing 65-85 mol % NiO powder with YSZ powderand sintering them in air at 1300° C. for 5 hours. The particle size ofthe metallic portion was 0.5-8 μm.

The use of nickel as the metallic component of a cermet anode isadvantageous, but its performance drops in short time, especially when adry hydrocarbon is the fuel, due to graphite formation.

R. J. Gorte et al., Adv. Mater., 2000, vol. 12, No. 19, 1465-1469,propose to substitute nickel with copper (Cu) in a cermet wherein theceramic portion is YSZ. Other components, including ceria (CeO₂), can beadded to the metallic portion. In this configuration the role of CeO₂ ismainly to provide catalytic activity for the oxidation of hydrocarbons.As shown in FIG. 4 a of this paper, the cell prepared with Cu butwithout ceria exhibits poor performance at 700° C., especially whenmethane is used as fuel.

C. Lu et al., High Temperature Materials, Proceedings volume 2002-5, Ed.S. C. Singhal, Pacific Northwest National Laboratory, Richland,Washington, USA, relate to a Cu-SDC (samaria-doped ceria) anodecomposite cell performing H₂ and butene fuels at 700° C.

From the above studies, it results that copper alone cannot be anefficient substitute for nickel as its performance is insufficient, inparticular with fuels such as dry hydrocarbons.

H. Kim et al., J. Electrochem. Soc., vol. 149 (3), A247-A250 (2002)examine the use of Cu—Ni alloys as anode component for the directoxidation of methane in SOFC at about 800° C. The ceramic portion, whichin this case is YSZ, is made by casting a tape with graphite poreformers over a green tape of YSZ without pore formers, firing thetwo-layered tape to about 1500° C. The porous anode layer was thenimpregnated with an aqueous solution of Ce(NO₃)₃.H₂O and calcinated atabout 500° C. to decompose the nitrate ions and form CeO₂. After theaddition of ceria, the porous layer was impregnated with a mixed,aqueous solution of Cu(NO₃)₂.H₂O and Ni(NO₃)₂—H₂O having the desiredCu:Ni ratio. Finally the wafer was again heated to about 500° C. in airto decompose the nitrates and reduced in flowing H₂ at about 900° C.

The Applicant has faced the problem of providing a solid oxide fuel cellwhich is able to show high efficiency and to maintain its performaceover time, particularly in terms of a low overpotential in a wide rangeof temperatures. Moreover, the fuel cell should be able to show theabove characteristics when fed with different fuels. Endurance ofperformance is particularly important when a dry hydrocarbon is used asfuel, since it tends to form graphite fibers on the metallic portion ofthe cermet anode, which eventually annihilate the fuel cell activity.

The Applicant has now found that by using a nickel alloy with one ormore metals as metallic portion of a cermet anode, and by reducing theaverage size of the particles constituting said alloy, the resultingSOFC shows enduring efficiency when fuelled with different fuels,including hydrogen and hydrocarbons, in a wide range of operatingtemperatures, and particularly at low temperatures, namely from 500° C.to 700° C. Particularly, when a dry hydrocarbon is used as fuel,deposition of graphite fibers is remarkably reduced. This result isparticularly surprising since a reduction of the average particle sizein the metallic component of the cermet would have been expected toincrease the catalytic activity also with respect to those sidereactions which cause formation of the graphite fibers.

The present invention thus relates to a solid oxide fuel cell including

-   -   a cathode;    -   at least an electrolyte membrane, and    -   an anode comprising a ceramic material and an alloy comprising        nickel and at least a second metal selected from aluminium,        titanium, molybdenum, cobalt, iron, chromium, copper, silicon,        tungsten, niobium, said alloy having an average particle size        not higher than 20 nm.

Preferably the anode of the invention comprises an alloy wherein saidalloy has an average particle size not higher than 16 nm. Morepreferably said average particle size is not lower than 1 nm.

The alloy of the anode of the invention can show a mean surface areahigher than 20 m²/g, preferably higher than 30 m²/g, and more preferablyhigher than 40 m²/g.

Preferably in the anode of the invention the alloy has a second metalcontent of from about 1% by weight to about 99% by weight, morepreferably, and even more preferably from about 40% by weight to about60% by weight.

Preferably in the anode of the present invention the alloy has a nickelcontent of from about 1% by weight to about 99% by weight, morepreferably from about 30% by weight to about 70% by weight, and evenmore preferably of about 50% by weight.

Preferably, said second metal is copper.

Said alloy can comprise an additional metal, for example, an elementbelonging to one of the classes from 3 to 13 of the periodic table ofelements according to Chemical and Engineering News, 63(5), 27, 1985,lanthanides series included.

The ceramic material of the anode of the invention can be selected fromyttria-stabilized zirconia (YSZ), cerium gadolinium oxide (CGO),samarium-doped ceria (SDC), mixed lanthanum and gallium oxides.Preferably the ceramic material is cerium gadolinium oxide (CGO).

The ceramic material of the anode of the present invention can show aparticle size not higher than 50 nm, preferably from about 1 to about 25nm.

Optionally, said ceramic material is doped with at least one cationselected from calcium, magnesium, strontium, lanthanum, yttrium,ytterbium, neodymium and dysprosium.

Optionally, the alloy of the invention comprises cerium oxide (CeO₂),optionally added with additives like cobalt.

The solid oxide fuel cell according to the present invention can beoperated in a wide range of temperatures, usually ranging from 450° C.to 800° C., and preferably from 500° C. to 700° C.

In another aspect the present invention relates to a cermet comprisingan alloy having a particle size not higher than 20 nm.

Both the metallic and the ceramic portion of the cermet anode of thepresent invention can be prepared from the corresponding metal salts,which may be compounded in a solid solution of the oxides thereof.

In a further aspect the present invention relates to a process forpreparing a cermet including a ceramic material and a metallic materialcomprising an alloy comprising nickel and at least a second metalselected from aluminium, titanium, molybdenum, cobalt, iron, chromium,copper, silicon, tungsten, niobium, said process comprising the stepsof:

-   -   a) producing a precursor of the metallic material;    -   b) producing the ceramic material;    -   c) combining said precursor and ceramic material to obtain a        composite;    -   d) reducing said composite wherein step a) comprises the phases        of        -   a-1) dissolving a hydrosoluble salt of Ni and a hydrosoluble            salt of a second metal in water;        -   a-2) adding a chelating agent to the solution resulting from            step a-1);        -   a-3) adding an oxidizing agent to the solution resulting            from step a-2);        -   a-4) isolating said precursor.

Optionally, the pH of the solution resulting from phase a-2) is adjustedat a value higher than about 5.

Preferably, phase d) is carried out by hydrogen at a temperature rangingbetween about 400° C. and about 1000° C., more preferably between about500° C. and about 800° C.

Step b) can include phases analogous to those from a-1) to a-4) of theprocess above, starting from the hydrosoluble salts corresponding to theoxide of the desired ceramic material. Phase a-4) can be followed by acrystallization step, for example at a temperature ranging between about200° C. and about 700° C., more preferably between about 300° C. andabout 500° C.

Preferably, the oxides of the present invention are prepared startingfrom hydrosoluble salts of the desired metals which are dissolved inwater and added with a chelating agent, for example, EDTA, oxalic,citric, acetic acid and the organic salts thereof, while maintaining thereaction mixture at a suitable pH, for example, higher than about 5.

Oxidation is then carried out, e.g. by addition of a peroxide, such ashydrogen peroxide, and co-precipitate of amorphous metal oxides isobtained.

This co-precipitate comprises very fine amorphous particlessubstantially free from any crystallographic ordering as revealed by XRD(X-ray diffraction) and TEM (transmission electron microscopy) analyses,as shown in the examples. The morphological and structural featuresobtained through this preferred method allow a superior extension of thethree-phase boundary (TPB) zone, advantageous to the performance of theSOFC.

After thermal treatment of the precursor, in air or inert atmosphere,for example helium, a solid solution of the metallic oxides intimatelyadmixed on an atomic scale, with fine particles size, is obtained. Theparticle size can range from about 3 to about 20 nm, preferably fromabout 4 to about 7 nm, more preferably of about 5 nm.

In the case the ceramic portion of the cermet anode according to theinvention is prepared through the above mentioned process,crystallization of the amorphous oxide precursor, for example at atemperature ranging between about 200° C. and about 700° C., morepreferably between about 300° C. and about 500° C., can yield a ceramicwith small particle size, for example ranging between about 6 and about2 nm.

The preparation of the cermet anode, i.e. the material system comprisinga metallic and a ceramic phase, can be carried out as follows. Amorphousmixed oxide precursor, obtained as said above, and a ceramic powder,preferably CGO or SDC, are admixed, and a slurry is prepared bydispersing the reactants in an organic solvent, for example isopropanol,and further treated with ultrasounds. The mixture is heated for solventevaporation, and a reduction, for example in H₂ atmosphere, is carriedout while heating, for example at a temperature ranging between about400° C. and about 1000° C., more preferably between about 500° C. andabout 800° C.

A solid oxide fuel cell of the invention can be prepared by applyingsaid slurry of composite on an electrolyte membrane comprising a ceramicmaterial, for example, CGO, SDC or YSZ.

A cathode for the solid oxide fuel cell of the invention can comprise aperovskite such as La_(1-x)Sr_(x)MnO_(3-δ), for example can be aLa_(0.6)Sr_(0.4)MnO₃/CGO.

The solid oxide fuel cell according to the invention displays greatflexibility in the choose of the fuel to be fed with. It can performs byfeeding the anode with a fuel selected from hydrogen; an alcohol such asmethanol, ethanol, propanol; a hydrocarbon in gaseous form such asmethane, ethane, butene; carbon dioxide, carbon monoxide, natural gas,reformed natural gas, biogas, syngas and mixture thereof, either in thepresence of water or substantially dry; or an hydrocarbon in liquidform, e.g. diesel, toluene, kerosene, jet fuels (JP-4, JP-5, JP-8, etc).Preferred by the present invention is substantially dry methane.

When a substantially dry fuel is fed to the anode, a direct oxidation iseffected in the solid oxide fuel cell of the invention. In the case ofdry methane, the reaction at the anode is the followingCH₄+4O²⁻→CO₂+2H₂O+8e ⁻

As already said above, the direct oxidation of a dry fuel such as a dryhydrocarbon yields coking phenomena (deposition of graphite fibers) atthe metallic portion of the cermet thus exhausting the catalyticactivity. The solid oxide fuel cell of the invention can perform bydirect oxidation of a dry fuel.

In another further aspect, the present invention relates to a method forproducing energy comprising the steps of:

feeding at least one fuel into an anode side of a solid oxide fuel cellcomprising an anode including a ceramic material and an alloy comprisingnickel and at least a second metal selected from aluminium, titanium,molybdenum, cobalt, iron, chromium, copper, silicon, tungsten, niobium,a cathode and at least an electrolyte membrane disposed between saidanode and said cathode;

feeding an oxidant into a cathode side of said solid oxide fuel cell;and

oxidizing said at least one fuel in said solid oxide fuel cell,resulting in production of energy.

The operating temperature of the solid oxide fuel cell of the inventioncan range from 450° C. to 900° C., preferably from 500° C. and 800° C.

An advantage provided by low operating temperatures, such thosepreferred by the present invention, is the reduction of No_(x) formationat the cathode. The formation of such undesired by-products is due tothe reaction of the nitrogen present in the air fed at the cathode side,such reaction being related to temperature increase.

In case of operating with reformed fuel, the fuel is internally reformedat the anode side.

The invention will be further illustrated hereinafter with reference tothe following examples and figures, wherein

FIGS. 1 a and 1 b schematically illustrate fuel cell power systems;

FIG. 2 illustrates XRD patterns of (a) amorphous oxide precursorNi_(0.58)Cu_(0.42)O, (b) crystalline oxide precursor Ni_(0.58)Cu_(0.42)Oand (c) Ni_(0.58)Cu_(0.42) bulk alloy;

FIG. 3 shows temperature reduction profiles with H₂ for (a) CuO, (b) NiOand (c) Ni_(0.58)Cu_(0.42)O crystalline precursor;

FIG. 4 illustrates catalytic activity vs temperature profile for methanesteam reforming experiments carried out for Ni_(0.58)Cu_(0.42) bulkalloy and Ni,Cu metallic mixture;

FIG. 5 shows XRD pattern of a Ni_(0.58)Cu_(0.42) (*)-CGO (o) cermet;

FIG. 6 shows XRD patterns of (a) crystalline Ni_(0.5)Cu_(0.50)-CGOcomposite after thermal treatment at 500° C. and (b) Ni_(0.5)Cu_(0.5)(*)-CGO (o) cermet after reduction at 900° C.; (#) corresponds to CuOphase;

FIG. 7 shows electrochemical polarisation curves forNi_(0.58)Cu_(0.42)-CGO cermet anode/CGO electrolyte interface in dry H₂and dry CH₄ in the temperature range between 650° and 800° C.;

FIG. 8 illustrates IR free electrochemical polarisation curves forNi_(0.58)Cu_(0.42)-CGO cermet anode/CGO electrolyte interface in dry H₂and dry CH₄ in the temperature range between 650° and 800° C.;

FIG. 9 illustrates a SEM micrograph of a Ni_(0.58)Cu_(0.42)-CGO anodiccermet layer of the invention, in cross-section;

FIGS. 10 a and 10 b show TEM images of, respectively, amorphous andcrystalline Ni_(0.58)Cu_(0.42)-CGO cermet according to the invention;

FIG. 11 show a low resolution TEM micrograph of Ni_(0.58)Cu_(0.42)-CGOanodic cermet layer, according to the invention, after 25 h at 250 mAcm⁻² in dry methane

FIGS. 1 a and 1 b schematically illustrate a solid oxide fuel cell powersystems. The solid oxide fuel cell (1) comprises an anode (2), a cathode(4) and an electrolyte membrane (3) disposed between them.

In FIG. 1 a fuel generally a hydrocarbon, is fed to be converted intohydrogen as described, e.g., in “Fuel Cell Handbook”, sixth edition,U.S. Dept. of Energy, 2002. Hydrogen is fed to the anode side of thesolid oxide fuel cell (1). Cathode (4) is fed with air.

The fuel cell (1) produces energy in form of heat and electric power.The heat can be used in a bottoming cycle or conveyed to fuel reformer(5). The electric power is produced as direct current (DC) and may beexploited as such or converted into alternate current (AC) via a powerconditioner (6).

FIG. 1 b shows a preferred embodiment of the invention. A substantiallydry fuel is fed to the anode (2) where direct oxidation is effected. Theheat can be used in a bottoming cycle. The direct current produced isexploited as such, for example in telecommunication systems.

In both the cases of FIGS. 1 a and 1 b, from anode (2) an effluent flowswhich can be composed by unreacted fuel and/or reaction product/s, forexample water and/or carbon dioxide in the case of FIG. 1 b.

EXAMPLE 1

Oxide Precursor and Alloy Preparation

-   a) NiCu alloys were prepared from reagent graded Ni(NO₃)₂.6H₂O and    Cu(NO₃)₂.6H₂O (Aldrich 99.99). Stoichiometric amounts of the metal    nitrates (2.86 g of Cu(NO₃)₂.6H₂O, 3.1 g of Ni(NO₃)₂.6H₂O) were    dissolved in distilled water (50 ml) and then complexed at 60° C.    with an aqueous so-lution of oxalic acid (9.5 g in 200 ml; Aldrich    99.99) at pH=6.5 adjusted with NaOH 0.1 N. The molar ratio between    complexing agent and the sum of the metal ions was 10. The complex    formation was monitored by UV spectroscopy. The solution was heated    to 80° C., and oxygen peroxide (400 ml, 20%, Carlo Erba) was then    dropwise added until complete formation of a precipitate. The    precipitate was filtrated, washed with distilled water, and dried at    120° C. K for 12 hours.-   b) The powder obtained at step a) was then calcinated at 500° C. in    air for 0.5 hour, to yield a crystalline phase.-   c) The crystalline phase of step b) was heated at 500° C. under H₂    atmosphere (H₂ for 30 min, 50 cc min⁻¹ g⁻¹ catalyst), in order to    reduce the oxide phase to a metallic phase.

In order to verify the phase composition and structure at steps a), b)and c), the powders were analyzed by X-ray fluorescence (XRF) and X-raydffraction (XRD) analyses.

XRF analysis (for composition) was carried out by Explorer Spectrome-ter(Bruker AXS, Germany) equipped with a Rh X-ray source. The instrumentwas equipped with 0.12° divergence collimator, LiF220 crystal analyzerand scintillation as well as proportional detectors.

XRD analysis (for structure and particle size determination) was carriedout under Bragg-Brentano configuration with CuKalpha radiation withXpert Diffractometer (Philips). The instrument was equipped withgraphite mono-chromator. The analysis range was selected from 5° to 100°2θ, the sweep rate was 1.5° min⁻¹. Results are shown in FIG. 2.

For each step product, the average particle size was calculated from XRDline broadening measurements using Scherrer equation. The results areset forth in Table 1, wherein the metal surface area was calculated fromthe particle size by the following formula:MSA(m²g⁻¹)=6 10⁴/(ρ·d);wherein ρ=(g cm⁻³) is density and d (Å) particle size.

The formation of the metal solid solution was checked by XRD, monitoringthe shifts on the diffraction peak assigned to the various reflectionsin particular the Ni (200) (JCPDS-ICCD data file, card no 4-8509) and Cu(200) (JCPDS-ICCD data file, card no 4-836) planes, and calculating thevariation in the lattice parameter of the metallic alloy structure fromVegard law. TABLE 1 Lattice parameter (a), particle size (d) and surfacearea (SA) of NiCuO_(x) and NiCu phases Lattice Phase/preparation stepparameter Particle size Surface area (ex. 1) (Ni:Cu) a_(fcc)/Å d/nmSA/m² g⁻¹ NiCuO_(x) 90:10 — <1.5 — amorphous 65:35 — <1.5 — (step a)58:42 — <1.5 — NiCuO_(x) 90:10 4.162 6.7 100.6 crystalline 65:35 4.1784.1 164.4 (step b) 58:42 4.183 4.3 156.8 NiCu alloy 90:10 3.521 15.942.4 (step c) 65:35 3.549 13.4 50.3 58:42 3.552 19.2 36.0

XRD analysis of the powder obtained from step a) did not show anyimportant crystallographic reflection but only an amorphous scattering,as from FIG. 2,a).

XRD analysis of the powder obtained from step b) showed thecharacteristic peaks of the faced centered cubic (fcc) structure of NiOshifted linearly as a function of the composition of the solid solution,as from FIG. 2,b). No evidence of monocline CuO phase was observedindicating that Cu atoms occupy the same crystallographic positions ofNi in the fcc structure with a random distribution. No evidence ofsuperlattice lines was detected.

XRD analysis of the powder obtained from step c) showed for the variouscompositions only the typical diffraction peaks of the fcc structure, asfrom FIG. 2,c). The lattice parameter varied linearly between pure Niand Cu metals as a function of relative composition.

Summarizing, at step a) an amorphous oxide with very small particle size(<1.5 nm) is formed (see FIG. 2.a), at step b) a crystalline oxide solidsolution is formed with a particle size around 5 nm (see FIG. 2.b), andat step c) (see FIG. 2.c) a single metallic phase is obtained (particlesize 10-20 nm).

EXAMPLE 2

Temperature Programmed Reduction (TPR) on NiO, CuO and NiCuO_(x) Oxides

TPR experiments were carried out in a tubular quartz microreactor. Atemperature sweep rate of 10° C. min⁻¹ was selected, the catalyst weightwas 5 mg and a TCD detector was used to determine H₂ consumption. Astream of 5% H₂ in Ar at a flow rate of 30 ml/min was fed to thereactor.

Three different samples, CuO (Aldrich), NiO (Aldrich) andNi_(0.58)Cu_(0.42)O_(x) were subjected to TPR experiments with H₂, inorder to compare their reduction kinetics and confirm the effectivenessof the process of the invention in preparing a metallic alloy.

The recorded profiles of FIG. 3 show that the onset for hydrogenconsumption and the respective peak maximum did occur on the mixedphases at a much lower temperatures with respect to the single phases:470 K (about 197° C.) for Ni_(0.58)Cu_(0.42)O_(x), 503 K (about 230° C.)for CuO and 626 K (about 353° C.) for NiO, respectively. Further, thereduction peak for the mixed Ni_(0.58)Cu_(0.42)O_(x) phases is much morenarrow, pointing for a faster reduction ki-netics, thus a higheraffinity for hydrogen, effective for reforming.

EXAMPLE 3

Catalytic Activity for Methane Oxidation (Reforming)

Methane reforming experiments were carried out in a packed bed tubularreactor (in-house made), where 15 mg of alloy catalyst of example 1,c)were diluted in 50 mg of quartz powder (Carlo Erba). Reactant feed wasH₂O/CH₄ (molar ratio 4:1), with a space velocity of 10⁵ h⁻¹.

Methane steam reforming experiments were carried out on aNi_(0.58)Cu_(0.42) bulk alloy example 1,c) and on a Ni,Cu metallicmixture of same compositions prepared by grinding and ultrasonicallymixing NiO and CuO oxides (Aldrich) followed by reduction under sameconditions of Example 1,c).

FIG. 4 shows that the onset temperature for the reaction on theNi_(0.58)Cu_(0.42) alloy is significantly lower than for that on theNi,Cu metallic mixture. The inflection point in the curve of catalyticactivity vs. temperature for Ni_(0.58)Cu_(0.42) alloy is about 50 K(200° C.) lower than that of Ni,Cu metallic mixture and 100 K lower thanthat reported in the literature for supported Ni catalysts (see C. T Au,H. Y. Wang, H. C. Wan, J. Catalysis 158 (1996) 343).

Elemental analysis was used to determine the carbon content in thecatalyst after catalytic and electrochemical experiments. Analyses werecarried out with a Carlo Erba CHNSO elemental analyser. No evidence ofcarbon deposition was found after reforming experiments on theNi_(0.58)Cu_(0.42) alloy.

EXAMPLE 4

Ni_(0.58)Cu_(0.42)-CGO (50:50 w/w) Cermet Preparation

Ce_(0.9)GdO_(1.95) (CGO) (prepared by co-precipitation of the cerium andgadolinium nitrates with oxalic acid at pH=6, followed by thermaldecomposition at 973K, as from Herle J. V., Horita T., Kawada T., SatoiN., Yokokawa H., Dokya M., Ceramic International, vol. 24, 229, 1998),and amorphous Ni_(0.58)Cu_(0.42)O (obtained in Example 1,a) wereintimately mixed in an agate mortar. Slurry was prepared by adding 10 mlof isopropyl alcohol to the powder mixture (116 mg CGO and 147 mg ofamorphous Ni_(0.58)Cu_(0.42)O), which was further ultrasonicated inorder to reduce the formation of agglomerates. The composite was thenheated to 423 K (about 150° C.) for solvent evaporation, followed byreduction at 773 K (about 500° C.) for 0.5 h under hydrogen flux. Theformation of the NiCu alloy on CGO was confirmed by X-ray diffraction(see FIG. 5 wherein * is for Ni_(0.58)Cu_(0.42), and ° is for CGO).

EXAMPLE 5

Preparation of a Ni_(0.5)Cu_(0.5)-CGO (50:50 ww) Cermet (ReferencePreparation)

1 g of CGO powder was impregnated according to what taught by H. Kim, etal., supra, with a 50 ml aqueous solution of Cu(NO₃)₂.H₂O (280 mg) andNi(NO₃)₂.H₂O (310 mg). Finally the layer was again heated to 500° C. andreduced in flowing H₂ at 900° C.

XRD analysis showed (FIG. 6) that the NiCu/CGO cermet prepared accordingto said method show particle size higher and surface area lower thanthat obtained in Example 4 (as from comparison with FIG. 5). Table 2sets forth the comparison by numbers. TABLE 2 Particle size (d) andsurface area (MSA) of NiCu alloys in NiCu-CGO cermets Preparationprocess d/nm Surface area (m²/g) Example 4 15 43 Example 5 26 26

EXAMPLE 6

Cell Preparation

A cell was fabricated having a CGO electrolyte, a LSM/CGO layer as acathode and a NiCu-CGO layer of Example 4 as an anode.

The CGO electrolyte (−500 μm, >90% theoretical density) was prepared byuniaxial pressing at 300 MPa of a Ce_(0.9)Gd_(0.1)O_(1.95) powderobtained as in Example 4. Before use for pellet preparation, the powderwas thermally treated at 1050° C. for 1 h. The pellet was thermallytreated at 1550° C. for 3 hrs.

As the cathode, a 30 μm LSM/CGO layer (50:50% wt) was deposited by apainting process on one side of the pellet and fired at 1250° C. for 1hour in air to assure good bonding to the electrolyte. The slurry usedwas composed of 100 mg CGO synthesized powder and 100 mg LSM(La_(0.6)Sr_(0.4)MnO₃, Praxair) both intimately mixed and dispersed in1.5 ml of isopropanol.

A 20 μm anodic cermet layer of amorphous Ni_(0.58)Cu_(0.42)O-crystallineCGO (50:50% wt) slurry was deposited by painting in one step on the CGOdense layer side of the CGO-LSM/CGO substrate. The slurry was preparedby dispersing 100 mg of amorphous Ni_(0.58)Cu_(0.42)O_(x) and 100 mg ofsynthesized CGO powders in 1.5 ml of isopropylalchool (carlo Erba). Thetotal amount of deposited metal phase was 2.5 mg/cm². This was dried at423 K (about 150° C.) to remove the solvent.

A 5 μm Au (Hereus) film, to be used as the anodic current collector inthe electrochemical cell, was then deposited by painting on the anodiclayer, and the whole assembly was heated at 150° C. for solventevaporation. Two Au wires on each side were allocated for samplingcurrent and potential.

Also, a 5 μm thin Pt (Enghelard) film, to be used as the cathodiccurrent collector in the electrochemical cell, was then deposited bypainting on the cathodic layer. A Pt reference electrode was allocatedon the cathodic side to allow operation of the device under half-cellconfiguration.

The cell (0.5 cm² active area) was mounted on an alumina tube and sealedwith quartz adhesive.

Finally the system was heated at 500° C. for 1 h in air to allowformation of a crystalline Ni_(0.58)Cu_(0.42)O_(x) oxide. Inert gas (He)was passed through the anode before hydrogen supply. An hydrogen streamflow rate (50 cc min⁻¹) was fed to the anode at 500° C. to assure thealloy formation.

EXAMPLE 7

Characterization in Half-Cell Configuration (Hydrogen Fuelled Anode)

Electrochemical evaluation of the performance of a solid oxide fuel cellaccording to Example 6, fed with hydrogen was carried out.

The hydrogen flow rate was 50-cc min⁻¹, and static air was used asoxidant. No humidification was used for the anode stream.

The cell was conditioned for at least 1 h in hydrogen at 800° C. beforerecording the polarization curves and ac-impedance spectra.

Electrochemical experiments were carried out both under galvanostaticand potentiostatic controls by using an AUTOLAB Ecochemiepotentiostat/galvanostat and impedance analyser. The polarization datawere collected under steady state conditions. Ac-impedance spectra werecollected in the range 1 MHz-1 mHz with a 20 mV rms sinusoidal signalunder open circuit conditions. A four-electrode configuration was usedin all cases. In half-cell experiments, one potential probe wasconnected to a non-polarized reference electrode and the overpotentialof the working electrode was measured against this reference.

Raw half-cell data of the Ni_(0.58)Cu_(0.42)O/CGO cermet anode/CGOelectrolyte interface indicated that this anode is active for theelectrochemical oxidation of dry H₂, as depicted in FIG. 7.

IR-free data (FIG. 8) show very low overpotentials, less than 50 mV forj=500 mA cm⁻². The curves recorded in presence of hydrogen show noactivation (kinetic) control. These data indicate that theNi_(0.58)Cu_(0.42)/CGO cermet anode combined with thin CGO electrolyteachieves high performances for the oxidation of dry hydrogen.

EXAMPLE 8

Characterization in Half-Cell Configuration (Dry Methane Fuelled Anode)

Electrochemical evaluation of the performance of a solid oxide fuel cellaccording to Example 6, fed with hydrogen was carried out.

Methane flow rate was 50 cc min⁻¹, and static air was used as oxidant.No humidification was used for the anode stream.

The cell was conditioned for at least 1 h in methane at 800° C. beforerecording the polarization curves and ac-impedance spectra.

Electrochemical experiments were carried out as in Example 8, buttesting the cell at three different temperatures, i.e. 800° C., 700° C.and 600° C., sequentially.

Raw half-cell data of the Ni_(0.58)Cu_(0.42)O/CGO cermet anode/CGOelectrolyte interface indicated that this anode is active for theelectrochemical oxidation of dry methane, as depicted in FIG. 7.

IR-free data (8) show for j=500 mA cm⁻² overpotentials of 250 and 350 mVvs. the reversible potential for H₂ oxidation at 800° C. and 700° C.respectively. The curves recorded in presence of methane show a slightactivation (kinetic) control that is not observed in presence ofhydrogen. These data indicate that the Ni_(0.58)Cu_(0.42)/CGO cermetanode combined with thin CGO electrolyte achieve high performances forthe oxidation of dry methane.

EXAMPLE 9

Analysis of Morphology and Carbon Deposition Characteristics of theAnodic Cermet

The overall process of formation of the Ni_(0.58)Cu_(0.42) alloy/CGOcermet in a cell prepared according to Example 6, and the modificationsoccurring after its exposure to dry methane, according to Example 8under electrochemical operation conditions were investigated by SEM(scanning electron microscopy), and TEM (transmission electronmicroscopy) analyses. SEM analysis (FIG. 9) shows uniform porosity ofthe anodic layer (upper part in the figure, on the membrane layer)during the preparation steps and after operation in the fuel cell.Further insights on the morphology were obtained by TEM analysis.

Distinction between Ni_(0.58)Cu_(0.42)O (or Ni_(0.58)Cu_(0.42) alloy)and CGO phases was possible by observing the lattice planes at highmagnification which are quite different in spacing between the twophases (FIG. 10 a).

TEM analysis of the amorphous Ni_(0.58)Cu_(0.42)O-crystalline CGO cermetprecursors clearly indicates a significant difference in terms ofparticle sizes between the two phases. After thermal treatment in air at500° C., the Ni_(0.58)Cu_(0.42)O phase became crystalline but there wasonly a slight increase in the particles size associated to this phasewhich are surrounding the larger CGO crystals (FIG. 10 b). After thermalreduction and subsequent operation under fuel cell conditions, thedimension of Ni_(0.58)Cu_(0.42) and CGO particles became similar (FIG.11), these particles join together maximizing the interfacecharacteristics. It has been demonstrated that the present inventionallows a superior extension of the three-phase boundary zone.

After operation of the anodic cermet at 800° C. under SOFC conditionswith a current density of 250 mA cm⁻² for 20 hrs, no evidence of carbonformation was observed by TEM on the surface of the alloy particles, asfrom FIG. 11.

Another cell, analogously prepared, was operated at 700° C. for 50hours. Also in this case no evidence of carbon deposition was detectedby TEM.

This result is opposite of that reported in Kim H., Lu C., Worrell W.L., Vohs J. M., Gorte R. J., J. Electrochem. Soc., 149 (3) A247-A250(2002) indicating a significant carbon deposition in the same timeinterval for an impregnated NiCu alloy layer under SOFC operation at800° C.

The cermet anode of the present invention is able to make the solidoxide fuel cell comprising it to operate with a wide selection of fuels.Especially said cermet, thanks to its characteristics of ionic andelectronic conductivity, and surface area and catalytic activity,permits the use of dry methane as fuel for electrochemical apparatus,without any sign of carbon deposition.

1-32. (canceled)
 33. A solid oxide fuel cell comprising: a cathode; atleast an electrolyte membrane, and an anode comprising a ceramicmaterial and an alloy comprising nickel and at least a second metalselected from aluminium, titanium, molybdenum, cobalt, iron, chromium,copper, silicon, tungsten and niobium, said alloy having an averageparticle size not higher than 20 nm.
 34. The solid oxide fuel cellaccording to claim 33 wherein said alloy has an average particle sizenot higher than 16 nm.
 35. The solid oxide fuel cell according to claim33, wherein said alloy has a mean surface area higher than 20 m²/g. 36.The solid oxide fuel cell according to claim 35, wherein said alloy hasa mean surface area higher than 30 m²/g.
 37. The solid oxide fuel cellaccording to claim 36, wherein said alloy has a mean surface area higherthan 40 m²/g.
 38. The solid oxide fuel cell according to claim 33,wherein said alloy has a second metal content of 1% by weight to 99% byweight.
 39. The solid oxide fuel cell according to claim 38 wherein saidalloy has a second metal content of 30% by weight to 70% by weight. 40.The solid oxide fuel cell according to claim 39, wherein said alloy hasa second metal content of 40% by weight to 60% by weight.
 41. The solidoxide fuel cell according to claim 33, wherein said alloy has a nickelcontent of 1% by weight to 99% by weight.
 42. The solid oxide fuel cellaccording to claim 38, wherein said alloy has a nickel content of 30% byweight to 70% by weight.
 43. The solid oxide fuel cell according toclaim 39, wherein said alloy has a nickel content of 40% by weight to60% by weight.
 44. The solid oxide fuel cell according to claim 33,wherein said second metal is copper.
 45. The solid oxide fuel cellaccording to claim 33, wherein said ceramic material is selected fromyttria-stabilized zirconia (YSZ), cerium gadolinium oxide (CGO),samarium-doped ceria (SDC), mixed lanthanum and gallium oxides.
 46. Thesolid oxide fuel cell according to claim 33, wherein said ceramicmaterial has a particle size not higher than 50 nm.
 47. The solid oxidefuel cell according to claim 33, wherein said ceramic material has aparticle size of 1 nm to 25 nm.
 48. The solid oxide fuel cell accordingto claim 33, wherein said ceramic material is doped with at least onecation selected from calcium, magnesium, strontium, lanthanum, yttrium,ytterbium, neodymium and dysprosium.
 49. The solid oxide fuel cellaccording to claim 45, wherein said ceramic material is ceriumgadolinium oxide (CGO).
 50. The solid oxide fuel cell according to claim33, wherein said cell performs in substantially dry hydrocarbon.
 51. Acermet comprising a ceramic material and an alloy having a particle sizenot higher than 20 nm.
 52. A process for preparing a cermet comprising aceramic material and a metallic material comprising an alloy comprisingnickel and at least a second metal selected from aluminum, titanium,molybdenum, cobalt, iron, chromium, copper, silicon, tungsten, andniobium, said process comprising the steps of: a) producing a precursorof the metallic material; b) producing the ceramic material; c)combining said precursor and ceramic material to obtain a composite andd) reducing said composite wherein step a) comprises the steps of a-1)dissolving a hydrosoluble salt of Ni and a hydrosoluble salt of a secondmetal in water; a-2) adding a chelating agent to the solution resultingfrom step a-1); a-3) adding an oxidizing agent to the solution resultingfrom step a-2); and a-4) isolating said precursor.
 53. The processaccording to claim 52, wherein step b) comprises steps analogous tosteps a-1) to a-4).
 54. The process according to claim 52, comprisingthe step of adjusting the pH of the solution resulting from step a-2) toa value higher than about
 5. 55. The process according to claim 52,wherein step d) is carried out with hydrogen at a temperature rangingbetween 400° C. and about 1000° C.
 56. A method for producing energycomprising the steps of: feeding at least one fuel into an anode side ofa solid oxide fuel cell comprising an anode comprising a ceramicmaterial and an alloy comprising nickel and at least a second metalselected from aluminium, titanium, molybdenum, cobalt, iron, chromium,copper, silicon, tungsten, and niobium, a cathode and at least anelectrolyte membrane disposed between said anode and said cathode;feeding an oxidant into a cathode side of said solid oxide fuel cell;and oxidizing said at least one fuel in said solid oxide fuel cell,resulting in production of energy.
 57. The method according to claim 56,wherein the at least one fuel is hydrogen.
 58. The method according toclaim 56, wherein the at least one fuel is an alcohol.
 59. The methodaccording to claim 56 wherein the at least one fuel is a hydrocarbon ingaseous form.
 60. The method according to claim 59, wherein thehydrocarbon is substantially dry.
 61. The method according to claim 56,wherein the at least one fuel is a hydrocarbon in liquid form.
 62. Themethod according to claim 56, wherein the at least one fuel issubstantially dry methane.
 63. The method according to claim 56, whereinthe fuel is internally reformed in the anode side.
 64. The methodaccording to claim 56, wherein the solid oxide fuel cell operates at atemperature ranging from 500° C. and 800° C.